Sometimes rosemary just dies... it can be temperamental like that. It hates cold winter winds and exposed places. My rosemary is doing the same, it's been in the same place now for three years with few problems but this winter has hit it hard. Take some softwood cuttings of the healthiest bits you have left, put in seed compost with a bag over the top to keep in the moisture and leave them in a coldframe or somewhere out of the way. They should root in a few weeks, then you'll have some good young plants just in case the old one dies.

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Dwell simply ~ love richly